Flaked lead acetate



Patented Jan. 26, 1932 UNITED STATESOPATENT OFFICE RALPH IE. LAWRENCE,OF WICKLIFFE, OHIO, ASSIGNOR TO THE GRASSELLI CHEMICAL" COMPANY, OFCLEVELAND, OHIO, A CORPORATION OF DELAWARE FLAKED LEAD ACETATE NoDrawing.

This invention relates to lead acetate in the form of thin flakes.

Neutral lead acetate crystallizes with 3 mols of water ofcrystallization. It is commonly made by concentrating a clear solutionof lead acetate to a high gravity, say 85 B., and then running the heavysyrup into pans. It forms under these circumstances super-cooled masseswhich remain for some time in the fluid state and then solidify as awhole to hard and compact, large size agglomerates. The further handlingof this product involves much manual labor in the removal from the pans,breaking up of the blocks and'packing which creates a seriousoccupational health hazard.

I have now found a process whereby lead acetate can be produced in aphysical form in which it is easy to handle, obviating the necessity ofbreaking it up or disintegrating it and doing away with much manuallabor and its inherent disadvantages. The so produced lead acetateappears in the form of thin, compact, co-herent flakes in which physicalform I am not aware that lead acetate has ever heretofore been produced,though it has in this form considerable practical advanof solidificationthat the product would break up on removal into an irregular powder withmuch dusting, which would create either a serious health hazard ornecessitate exten sive dust collecting equipment.

I have found that by inducing the crystallization of concentrated leadacetate liquor films solidification takes place gradually, passingthrough a stage where the lead ace- Applieation filed October 14, 1929.Serial No. 399,710.

tate has a waxy consistency. The film can atthis stage easily be scrapedoff, whereby it breaks up into small, co-herent shavings like flakes,which do not dust, and solidify finally into hard and compact individualflakes.

A technically very convenient manner of inducing the solidification of asyrupy lead acetate film is to bring it into contact with solid leadacetate'and I found that this is particularly easily achieved by firstcoating a cooling surface with a thin layer of solid lead. acetate; thesyrupy melt of additional lead acetate applied thereto solidifiesgradually passing through a waxy state of con sistency. 'A thin film ofwaxy lead acetate is so formed. It does not, while in this state adherevery firmly to the base layer of solid acetate; when scraped ,ofi fromsaid solid layer it separates into non-dusting, nonsticky soft flakes,or shavings,'which soon solidify into hard, coherent flakes of more orless regular shape, usually about one millimeter thick, severalmillimeters long and a :few millimeters wide.

The product in this flake form weighs, when packed, from to TOlbs; percubic foot packing space; the flakes are easily soluble and convenientlyhandled by the consumer.

The flaking of lead acetate according to my novel process isconveniently achieved on so called drum soli-difiers or drum coolers.This type of apparatus consists in its essential )illtS of a feedindevice such as a trou h or feeding channel containing the liquid to besolidified, of a rotating cylinder which is in contact with the liquidin the feeder and on rotation picks up some of the liquid which adheresto its surface and solidifies thereon in contact with the atmosphere andof a scrap ing device which removes the solidified material from thesurface of the drum. Provision is usually made to cool the inside of thedrum with a gaseous or liquid cooling fluid. .In preparing my novelflaked product I used a solution of lead acetate of 1%. at 100 C. Someof this liquor was poured upon the surface of a rotating cooling drumand rub-bed over the surface of the drum by means of a brush forminguniform layer thereon which crystallized and adhered to the drum.

2. Lead acetate in the form of hard, com- The knife edge of the scraperarrangement pact and co-herent flakes which weigh, when was then soadjusted as to leave a thin coat packed from about 50 to 70 lbs. percubic of this original, solid lead acetate on the foot.

drum.

A very convenientmanner of feeding the concentrated lead acetate liquorupon the drum cooler coated as described above with a thin layer ofsolid lead acetate was found to consist in running a stream oft-theliquor down an incline which ends in a piece of sheet steel fittedclosely to the layer of solid acetate, at the back, underside of thedrum, tangent to the surface and parallelto the axis of the drum. Theacetate liquor accumulates in the channel formed between the steel sheetand the drum and is from there picked up during revolution forming aliquid film upon the original base layer of solid acetate and solidifiesuniformly thereon.

The 85 B. acetate liquor when fed in this manner to the druinstarted tosolidify after a few seconds in contact with the solid acetate, whichserves as a seeder. The speed of revolution of the drum and the coolingwere adjusted to give the lead acetate film about 23seconds time betweenits formation at the feeder and its removal by the scraper. It hadduring this time solidified to a waxy, nonsticky consistency and itbroke oil atthe knife in the form of soft, non-sticking flakes which ina few minutes after leaving the scraper setto compact, hard flakes. Thepacked weight of the product from this particular run was 67 lbs. percubic foot; it analyzed 55.8% Pb, whereas the theory for Pb (0 1 1 0 3HO is 541670. indicating a slight drying action during the process,which, however, is not objectionable. The packed weight of the productmade by my process varies generally between the limits of about 50 and 70 lbs. per cubic foot. The color of the product depends upon the purityof the liquor used, and when this is of good quality a snow white flakedlead acetate is obtained.

The performance of my novel process can be varied in various wayswithout departing from the spirit of my invention provided thesolidification of the lead acetate liquor is so conducted that it takesplace gradually through a stage where it has a waxy, nonstickyconsistency. at which stage the acetate is separated into flakes.

It is further understood that the term lead acetate used herein with itsusual commercial meaning of neutral lead acetate containing in theneighborhood of 3 mols of water of crystallization.

The process of producing flakes of lead acetate as disclosed herein isclaimed in my divisional application Serial #513,784, filed February 5,1931.

I claim:

1. Lead acetate in the form of hard, coinpact and coherent flakes.

In testimony whereof, I aflix my signature.

RALPH LAlVRENCE.

